This application is in response to the RFA: AI-18-023 ?Immune Mechanisms at the Maternal-Fetal Interface?. The trophoblast represents the first point of contact between the blastocyst and the maternal decidua and has an active role in shaping the immunological milieu at the implantation site. Trophoblast cells express pattern recognition receptors (PRR) that function as ?sensors? of the surrounding environment. Through these receptors, the trophoblast can recognize bacteria, viruses, and other microbes as well as dying cells and damaged tissue. Type I IFN production is known to be a characteristic of the placenta in several species, including humans; and IFN? is the predominant class, especially during the first trimester. In the context of pregnancy, we have shown that loss of IFN? signaling in the placenta leads to: 1) uncontrolled viral replication and fetal viral infection, 2) maternal mortality and 3) hypersensitivity to bacterial products; suggesting a critical role of IFN? signaling in the protection of pregnancy. Our central hypothesis is that placental IFN? signaling is critical for the protection of the fetus and the mother during viral infections and because its ability to modulate TLRs? responses can function as a major immune modulatory factor at the implantation site. The premise for this proposal is that in the trophoblast, there is an intrinsic cross talk between TLR2/4 and IFN? pathway that provides protection against infection, but also prevents potential detrimental pro- inflammatory responses by inhibiting transcription of NF-?B regulated inflammatory cytokines. In addition, we have identified a novel mechanism of immune regulation in the trophoblast involving the TAM receptors, specifically the Axl receptor. The significance of these findings is in our premise that pathogens might hijack components of these pathways for purposes of microbial immune evasion. Pathogens such as viruses might inhibit IFN? and enhance inflammation necessary for viral replication; or bacteria/parasites might promote IFN? expression to inhibit NF?B-inflammation for cell infection. Our specific aims are: Aim 1. Determine how IFN? interacts with Axl to regulate trophoblast inflammation. Aim 2. To characterize the mechanism by which IFNs and TAMs regulate transcription of NF-?B- dependent genes in the trophoblast. Aim 3. Define the impact of viral infections on the cross talk between Axl-IFN?-TLR2/4 in animal models. Upon completion of these aims we will have a better understanding of the essential role for IFN? and type I IFN receptor signaling in host responses to microbial infections during pregnancy. We will elucidate how IFN?, and its regulatory pathways, such as TAM receptors, protect the fetus not only against viral infections but also prevents detrimental inflammatory responses. The outcome of these studies not only will enhance our understanding of the complexity of immune regulation at the maternal/fetal interface but also will provides novel opportunities for the identification of predictive markers and new therapeutic approaches by modulating IFN?/TAM receptor signaling to protect pregnant women at risk to viral infections or during pandemics.